In numerically controlled lathes such a turret head serves for the reception of a plurality of preset tools which project beyond the front end surface of the cylindrical rotary disk. The axis of rotation of the rotary disk is usually disposed horizontally and parallel to the axis of the workpiece spindle. A plurality of rotary disks are provided which are also interchangeable.
In order to enable the preset tools to be easily interchanged on the rotary disk, a "cylindrical shank tool system" (VDI-Richtlinien, VDI 3425, page 2, Nov. 1972) has been developed. In this system, the tool holder provided for receiving each tool has a cylindrical shank which is formed on one side with a flat surface and with a set of teeth extending transversely to the axis of the shank. The cylindrical shank can be inserted in the respective shank-receiving bore of the rotary disk. Moreover, there is arranged for sliding movement in the rotary disk a clamping element which by means of a set of teeth provided thereon meshes with the set of teeth on the shank. By means of this clamping element the toolholder will be pressed radially so that its shank enters the respective bore and its annular surface engages the end surface of the rotary disk. Although the shank and the receiving bore interengage as a close fit, a slight amount of play must always be present between the shank and the shank-receiving bore in order to enable the shank to be slid into the shank-receiving bore without the use of undue force. By means of the clamping element a force is exerted which is directed transversely to the axis of the shank and acts unilaterally against it. The shank is thus pressed against that side of the shank-receiving bore which is remote from the clamping element. The result of this is that, when the tool holder is clamped tight, the axis of its shank is offset eccentrically and parallel with respect to the axis of the shank-receiving bore. The accuracy of the assembly operation and the accuracy with which it can be repeated and hence also the accuracy of manufacture are thus negatively influenced. Moreover, the pressure of the shank against part of the wall of the shank-receiving bore results in substantial frictional force being exerted between the two parts and between the two sets of teeth that are in mesh with each other. This substantial frictional force prevents axial displacement of the shank in the shank-receiving bore, so that the annular surface of the toolholder is not pressed with sufficient force or often not in fact pressed at all against the end surface of the rotary disk. The transverse forces acting on the tool are then insufficiently transmitted or no longer transmitted at all from the annular surface to the end surface of the rotary disk and the transmission of force takes place only through the relatively small diameter shank. In addition, the torque must be transmitted solely from the clamping element to the shank, which can lead to deformation of the two sets of teeth. A further disadvantage of this known connection between the tool holder and the rotary disk consists in the fact that the shank-receiving bores in the rotary disk are all made of equal size. If toolholders having a smaller or larger shank diameter need to be connected to the rotary disk, this is only possible with the interposition of adaptors. The interposition of adapters, however, increases the extent of projection of the tool, i.e. the tool is located at a greater distance from the end surface of the rotary disk. This means that there is not only a loss of stability, but also inter alia that there are obstacles in the working space and movement restrictions. Furthermore, it may happen that the connection between the tool holder and the rotary disk will be damaged as a result of some kind of unforeseeable overload. In this case, the entire rotary disk must then usually be replaced by a new one. Moreover, in the known "cylindrical shank tool system", the shank and hence also the shank-receiving bore must have a relatively great length, which is more than one and a half times as great as the diameter of the shank. Thus, an increased consumption of material results during the manufacture of the tool holder and the weight of the latter is also increased. The relatively great length of the shank can moreover be disadvantageous in relation to an automatic interchange of the tool holders.
The invention has for its basic object to improve a turret head for a lathe and a tool holder suitable for use therewith, which are of the kind initially referred to, as follows, i.e. so that, when the tool holder is clamped tightly to the rotary disk, no radial displacement of the axes of the toolholder and the receiving bore will take place and the annular surface will be pressed with a considerable prestressing force against the end surface of the rotary disk which is fixed for rotation with the spindle, in order thereby on the one hand to improve the accuracy of the assembly and of the mechanical functioning of the apparatus and on the other hand to ensure that a maximum proportion of the torque will be transmitted by frictional contact from the rotary disk to the annular surface, and furthermore to provide a connection between the tool holder and the rotary disk which is resistant to bending and non-oscillating and the component parts of which can easily be replaced in the event of their being damaged. In addition, it must be possible, if necessary, to connect tools to the rotary disk so that they project the least possible distance from the latter.
This is achieved according to the invention in that the rotary disk has a cylindrical insert-receiving recess disposed concentrically with each shank-receiving bore, that for each insert-receiving recess there is provided an insert disk which is removably insertable therein and concentrically within which is located the respective shank-receiving bore, that each insert disk has, in the region of the cylindrical shank-receiving bore, two diametrically opposite, radially extending screw-threaded bores, an inner clamping screw with a conical recess being screwed into one of the screw-threaded bores which is located more inwardly in relation to the axis of the rotary disk and an outer clamping screw with a conical end part being screwed into the other screw-threaded bore which is located more outwardly in relation to the said axis, that the shank of each tool holder has a transverse bore with a clamping bolt srranged for radial sliding movement therein and provided at one of its ends with a conical end part which cooperates with the conical recess in the inner clamping screw and is provided at its other end with a conical recess which is arranged to cooperate with the conical end part of the outer clamping screw and that the distance of the axis of the screw-threaded bores from the end surface of the insert disk is somewhat greater than the distance of the axis of the transverse bore from the annular surface, so that, when the outer clamping screw is tightened, it acts against the clamping bolt in a direction to cause pressure of the annular surface and the end surface of the insert disk against each other.
The invention also originates from the concept of not allowing the shank of the tool holder to engage directly in the rotary disk, but arranging instead for it to engage in the shank-receiving bore in an insert disk which is itself let into the rotary disk and loosely connected therewith. Between the shank and the shank-receiving bore further special clamping elements are provided which are known per se in connection with a boring tool (DE-PS No. 31 08 439).
As a result of the insert disk being let into a corresponding insert-receiving recess in the rotary disk a connection is obtained between the tool holder and the rotary disk which is structurally very short and hence to a considerable extent vibrationless. The insert disks themselves as well as the shank-receiving bores provided therein, can be produced with greater accuracy, so that an improvement in the accuracy of manufacture is obtained. As a result of the separate manufacture of the insert disks, the formation of the clamped connection between the shank of the tool holder and the rotary disk is also simplified. In particular, if any of the parts of the connecting and clamping elements are damaged, these parts can easily be replaced and there is no need for the entire rotary disk to be replaced. By changing insert disks for others having greater or smaller diameter shank-receiving bores, it is also possible to insert tool holders with a larger or smaller shank diameter directly into the insert disks without the interposition of adapters. By the use of the connecting device disclosed in the above mentioned DE-PS No. 31 08 439, which in that specification serves only for connecting pats of tools to one another, further additional advantages are obtained. Compared with the conventional connection initially referred to between toolholder and rotary disk, an extraordinarily stable and accurate connection is provided between these two parts. The use of a radially displaceable clamping bolt prevents the shank from being urged radially towards one side in the shank-receiving bore when the outer clamping screw is tightened. Since no radial forces act on the shank, no displacement of the axis of the shank occurs with respect to the axis of the shank-receiving bore, so that both of these axes are always in precise axial alignment. A high degree of accuracy of assembly and reproduction is also ensured. Due to the elimination of lateral pressure of the shank against the wall of the shank-receiving bore, it is further ensured that the forces exerted by the clamping screws will be transmitted via the clamping bolt to the shank. The clamping force of the radially outer clamping screw produces in the radially inner clamping screw an equal but oppositely acting reaction force, whereby the clamping force of the outer clamping screw is doubled. Due to the conical end parts and recesses, the radially acting clamping forces of the clamping screws produce axially acting forces. As a result of the axial offsetting of the common axis of the clamping screws and the clamping bolt, the latter is also displaced axially by the axially acting force components and consequently presses the annular surface with an increased loading force against the end surface of the rotary disk. Due to the intense and uniform pressure of the said annular surface against the said end surface, a greater proportion of the torque is transmitted, via these surfaces by frictional engagement. The rest of the torque is transmitted through the clamping screws and the clamping bolt. It is furthermore important that, when there is good contact between the said annular surface and the said end surface, the forces which act transversely on the tool will be transmitted over a relatively large diameter from these two surfaces. Consequently, the accuracy of manufacture is increased and the danger of vibration of the tool is reduced. In addition, higher cutting capacities and hence shorter working times are obtained.